First Alert SMI100 Ionization Smoke Alarm — Battery Operated (Single Sensor)
$16.99
$19.99
Final price set by Amazon · may vary
EDITORIAL REVIEW: 4.5/5 WC Safety Review — First Alert SMI100 Ionization Smoke Alarm — Battery Operated Editorial assessment by the WC Safety Editorial Team, based on published First Alert specifications and categ...
Key Features
- First Alert's Precision Detection advanced sensing technology complies with new industry standards to reduce cooking nuisance alarms and provides early warning in the event of a home fire emergency
- Battery-operated alarm allows for easy installation and maintenance
- Front access battery compartment makes for easy battery replacements
- End-of-life warning lets you know when its time to replace the alarm
- Test/silence button for efficient testing to ensure alarm is working properly
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EDITORIAL REVIEW: 4.5/5 WC Safety Review — First Alert SMI100 Ionization Smoke Alarm — Battery Operated
Editorial assessment by the WC Safety Editorial Team, based on published First Alert specifications and category fit. We did not laboratory-test this product.
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First Alert SMI100 Ionization Smoke Alarm — Battery Operated (Single Sensor) Overview
The First Alert SMI100 is a battery-operated ionization smoke alarm designed for early detection of fast-flaming fires. Ionization sensing reacts quickly to the small, fast-moving smoke particles given off by flaming combustion — burning paper, cooking grease, and flammable liquids — making this sensor type well suited to spaces where that fire risk is highest.
Because the SMI100 runs on battery power, there is no wiring to deal with: mount it on the ceiling or high on a wall and you have working coverage in minutes. That makes it an easy way to add a smoke alarm to a bedroom, hallway, or an upper or lower level that lacks protection. Fire-safety guidance calls for a smoke alarm on every level of the home and inside and near each sleeping area, so a simple battery unit like this fills gaps without an electrician.
One thing to be clear about: the SMI100 is a smoke alarm only. It does not sense carbon monoxide. Carbon monoxide is a colorless, odorless gas, and detecting it requires a dedicated CO detector or a combination smoke/CO alarm. For whole-home coverage, pair this smoke alarm with separate CO protection. Compare options across our smoke detectors and review top picks in our best smoke detectors guide. Like all smoke alarms, plan to replace the unit roughly every 10 years and test it regularly using our how to test a smoke & CO alarm walkthrough.
What It Is Built For
| Use case | Fit | Buyer guidance |
|---|---|---|
| Bedrooms and inside sleeping areas | Strong fit | Mount inside each bedroom; ionization sensing gives fast warning for flaming fires near sleeping occupants. |
| Hallways outside sleeping areas | Strong fit | Install in the hallway serving bedrooms so an alarm wakes everyone on that level. |
| Adding coverage to an unprotected level | Strong fit | Battery power means no wiring — ideal for basements, attics, or extra floors that lack an alarm. |
| Kitchen-area flaming-fire risk | Good fit | Ionization responds well to grease and flaming fires, but place at least 10 ft from cooking appliances to limit nuisance alarms. |
| Carbon monoxide detection | Not suitable | This is a smoke-only alarm. Use a dedicated CO detector or a combination smoke/CO alarm for carbon monoxide. |
| Smoldering-fire-prone rooms | Limited fit | Ionization is slower on smoldering fires; add a photoelectric alarm in living rooms and near upholstered furniture for balanced coverage. |
A smoke alarm and a carbon-monoxide alarm detect different hazards — install both (or a combination unit) on every level and near each sleeping area, and interconnect them where possible. Test monthly and replace at the unit's end-of-life date (CO sensors typically last 5–10 years; smoke alarms about 10). Carbon monoxide is colorless and odorless, so a working alarm is your only warning — look for UL 2034 (CO) / UL 217 (smoke) listing. See how to test a smoke & CO alarm and the CO detector placement guide.
Pros & Cons
Pros
- Battery operated — installs anywhere with no wiring or electrician
- Ionization sensor responds fast to flaming, fast-spreading fires
- Single-sensor design is simple to mount and maintain
- Compact unit suits bedrooms, hallways, and added-coverage spots
- Trusted First Alert smoke-alarm build
Cons
- Smoke-only — does not detect carbon monoxide
- Ionization is slower to react to smoldering fires than photoelectric
- Standalone battery unit does not interconnect with other alarms
- Battery requires periodic replacement and the alarm needs ~10-year replacement
How It Compares
Within First Alert's residential lineup, the SMI100 is the simplest tier: a single-sensor, battery-operated ionization smoke detector with no CO sensing, no wiring, and no interconnect. If you need carbon monoxide protection in the same unit, step up to the plug-in SMCO100V-AC, which combines smoke and CO sensing — see our combination smoke/CO alarms. For whole-house wiring with smart features, the hardwired SMCO600NV-AC SC5 interconnects across the home. For a comparable battery ionization alternative from another brand, the kidde i9010 ionization smoke alarm 9v battery covers the same fast-flaming use case, while the kidde 10sdr battery operated smoke alarm is another battery option to weigh.
Specifications
| Detects | Smoke only (not carbon monoxide) |
| Sensing type | Ionization — best for fast-flaming fires |
| Power | Battery operated (standalone) |
| Interconnect | No — standalone unit |
| Display | None (audible alarm) |
| Mounting | Ceiling or high wall |
| Recommended replacement | Approximately every 10 years (smoke alarm) |
| Brand / Model | First Alert SMI100 |
Related Resources
CO detectors smoke detectors carbon monoxide alarms combination smoke/CO alarms gas detectors best CO detectors best smoke detectors CO detector placement guide how to test a smoke & CO alarm kidde kn copp b lpm battery carbon monox
Frequently Asked Questions
Does the First Alert SMI100 detect carbon monoxide?
No. The SMI100 is a smoke-only ionization alarm and does not sense carbon monoxide. Carbon monoxide is colorless and odorless, so you need a dedicated CO detector or a combination smoke/CO alarm for that protection. Browse options in our CO detectors collection at /collections/co-detectors.
What kind of fire is the ionization sensor best for?
Ionization sensing reacts fastest to fast-flaming fires — burning paper, grease, and flammable liquids that produce small, fast-moving smoke particles. For smoldering fires (slow, smoky fires from upholstery or wiring), a photoelectric alarm reacts sooner, so many homes use both sensor types.
Is the SMI100 battery operated or does it need wiring?
It is battery operated and standalone — no wiring or electrician required. You mount it on the ceiling or high on a wall and it is ready to protect the space, which makes it easy to add coverage where there is no existing alarm.
Where should I install this smoke alarm?
Put a smoke alarm on every level of the home and inside and just outside each sleeping area. Mount the SMI100 on the ceiling or high on a wall, away from cooking appliances and air vents that can cause nuisance alarms. Bedrooms and hallways are ideal spots.
Can the SMI100 interconnect with my other alarms?
No. The SMI100 is a standalone battery unit and does not interconnect, so when it alarms it sounds on its own. If you want every alarm to sound together, look at a hardwired interconnect model instead — see our smoke detectors collection at /collections/smoke-detectors.
How often should I replace the SMI100?
Smoke alarms should be replaced about every 10 years from the date of manufacture, regardless of how they test. Replace the battery as needed in between, and replace the entire alarm at the 10-year mark to keep the sensor reliable.
How do I test the alarm after installing it?
Press and hold the test button until the alarm sounds, and test regularly (a monthly check is a good habit). Our step-by-step guide walks through testing both smoke and CO alarms at /blogs/how-to-guide/how-to-test-a-smoke-and-co-alarm.
Can I use the SMI100 in a kitchen?
Ionization alarms respond well to flaming and grease fires common in kitchens, but mount it at least about 10 feet from cooking appliances to reduce nuisance alarms from steam and smoke. For the cooking area itself, many homeowners prefer placement just outside the kitchen.
Should I also have a carbon monoxide alarm?
Yes — because the SMI100 does not detect CO, you should add a separate carbon monoxide alarm, especially if you have fuel-burning appliances, a fireplace, or an attached garage. See our carbon monoxide alarms at /collections/carbon-monoxide-alarms-detectors or our best CO detectors guide at /blogs/guides/best-carbon-monoxide-detector-2026.
How is the SMI100 different from a combination smoke and CO alarm?
The SMI100 only senses smoke. A combination alarm adds a carbon monoxide sensor in the same housing, so it warns about both threats from one unit. If you want both in one device, see our combination smoke/CO alarms at /collections/combo-smoke-co-alarms.
Does this alarm have a digital display?
No. The SMI100 is a straightforward audible smoke alarm without a digital readout. Digital displays are typically found on carbon monoxide and combination alarms that show CO levels in parts per million.
How many smoke alarms do I need in my home?
Fire-safety guidance calls for a smoke alarm on every level, inside each bedroom, and outside each sleeping area. Because the SMI100 installs without wiring, it is an easy way to reach that coverage — compare top picks in our best smoke detectors guide at /blogs/guides/best-smoke-detectors-2026.
Written by Steven Eaton, WC Safety Editorial. Specifications sourced from First Alert published data. Compare the range in carbon monoxide & smoke alarms.
WC Safety is an independent PPE retailer and Amazon Associate; no paid placement. Match the product to your specific hazard and follow your site PPE program.
Brand / Vendor
First Alert
Model / SKU
SMI100
Product Type
Smoke Detector
Condition
New
MPN
SMI100
Price
$16.99 (Amazon)
Rating
4.88 / 5 — 8 reviews
Availability
Check current availability on Amazon
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Verified Buyer Reviews
Customer Reviews
★★★★★4.9 / 5· 8 verified reviews
★★★★☆
4.0 out of 5 stars
A great, cheap option for a smoke detector! Installed onto the wall super easy. One issue, is the battery compartment can catch when trying to install the battery, but a little pressure and it clicks into place (without breaking any plastic, thankfully).
Anonymous · 2026-04-30 · ✓ Verified Buyer
★★★★★
5.0 out of 5 stars
These aren't interconnected, and are powered by battery only. But they do the job as described and are a lower cost option to replace the more costly interconnected "wired" models.
Anonymous · 2026-04-30 · ✓ Verified Buyer
★★★★★
5.0 out of 5 stars
These are perfect. Easy installation and easy to monitor 👌.
Anonymous · 2026-04-30 · ✓ Verified Buyer
★★★★★
5.0 out of 5 stars
I just installed these 2 First Alert smoke detectors, so I can’t give you a long time use review, but I’m happy with my purchase. These replaced two 10 year-old similar First Alert smoke detectors that had reached their expiration date. I was very pleased with those, which is why I looked for the same smoke detectors. I couldn’t find the exact same ones, so I replaced with these, which look similar and are basic like the first pair. Although the size of the new ones are a little bit smaller than the ones they replaced, I was pleased to find that the new brackets fit the 2 screws I already had in the walls from the old ones. I was concerned that I would be patching and drilling, but I didn’t have to, so installation was easy peezy. The other thing that is different on the new ones is that the batteries are 9 V versus the AAs for the old ones. I prefer AAs because it’s a battery that I always have around the house and they are easy to come by and inexpensive, relatively speaking. However, the new detectors came with batteries, so I don’t have to worry about replacing them for another year.
Anonymous · 2026-04-30 · ✓ Verified Buyer
★★★★★
5.0 out of 5 stars
I recently purchased the First Alert SMI100 smoke alarms and I’m really happy with them. Installation was incredibly easy since they are battery operated, so there was no wiring needed. I had both alarms mounted in just a few minutes. The design is simple and clean, and the front battery compartment makes it easy to change the battery without taking the whole unit down. I also like the test/silence button on the front because it makes testing the alarm quick and simple. The alarm itself is loud enough that you would definitely hear it throughout the house, which is exactly what you want for safety. The detectors use updated sensing technology designed to give early warning of fires while reducing nuisance alarms from things like cooking smoke.Overall, these smoke alarms give me peace of mind knowing my home has reliable protection. They were affordable, easy to install, and work exactly as expected. I would definitely recommend them to anyone looking for a simple and dependable smoke alarm.
Anonymous · 2026-04-30 · ✓ Verified Buyer
★★★★★
5.0 out of 5 stars
So far so good, we've had these fire alarms for about a year now and the one near the kitchen we replaced the batteries about 6 months ago, and the other one we just did for the first time. The one near the kitchen has been triggered a few times due to various baking mishaps so that makes sense I guess, definitely loud enough to wake you if necessary. Its a bit of a pain to change the batteries but that's life. Seems to be reliable and that's all I really care about. Install was simple enough.
Anonymous · 2026-04-30 · ✓ Verified Buyer
★★★★★
5.0 out of 5 stars
I've been using this brand for decades and I'm glad they took things to a little higher level for the most basic even though it costs a little more . For some reason the ones I have that were the old basic unit would last about 3 years then start beeping like the battery was dead even with a new battery , thus needed to be replaced . This unit is easier to blow off the sensor and hopefully that'll help it last longer . Nothing more annoying than that irregularly timed beep at oh dark thirty and not knowing which one it is because of the irregularity of when it beeps . I have a smoke detector in every bedroom, laundry , kitchen, den and hallways for a total of 8 in the home. Not knowing which one needs attention sucks . This one did need for me to change the frame it fits in but the screws stayed in the same spots so it was super quick to change out .
Anonymous · 2026-04-30 · ✓ Verified Buyer
★★★★★
5.0 out of 5 stars
This First Alert smoke alarm is clearly the standard. Works reliably, is a powerhouse in a small size. It can be installed easily with a simple nail or screw without using the wall attachment materials included. It has a very loud piercing notification signal which is exactly what I needed to wake kids out of bed and get them started on how I have trained them if there is a fire. This unit was a replacement for a unit I have had for nearly 10 years. These smoke alarms are reliable.
Anonymous · 2026-04-30 · ✓ Verified Buyer
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